Etching procedures are used extensively in the fabrication of semiconductor devices. They are used to alter the physical dimensions of semiconductor material and to cut through semiconductor material as in cutting up semiconductor disks into individual chips. They are also used to provide holes and slices in semiconductor materials. It is extremely important to provide reliable and flexible etching procedures in the fabrication of semiconductor devices.
With advancing technology in semiconductor devices, the requirements for greater precision and resolution in fabrication procedures has become greater and greater. In particular in etching procedures, the chemical reaction is usually isotropic or preferential with respect to certain crystal planes and etching advances in all directions or preferentially along these planes. This limits the usefulness of etching procedures because the isotropic nature of the etching reaction limits precision and resolution.
Photoetching is highly attractive as a fabrication procedure for semiconductors because the chemical reaction is confined to the part of the surface illuminated by radiation. Thus, the radiation can be used to confine the etching reaction to the area desired. This can result in anisotropic etching. Semiconductor photoetching is described in a number of references including, for example, "Photoetching and Plating of Gallium Arsenide" by R. W. Haisty, Journal of the Electrochemical Society, 108, page 790 (August 1961); "Selective Photoetching of Gallium Arsenide" by F. Kuhnenfeld, J. Electrochem. Soc., 119, page 1063 (August 1972); and "Photoetching of InP Mesas for Production of mm-Wave Transferred-Electron Oscillators" by D. Lubzens, Electronics Letters, 13, page 171 (1977).
These references describe photoelectrochemical etching of n-type GaAs and InP by oxidative decomposition. Here, holes are created by exposure of the semiconductor to radiation and these holes cause oxidation of the GaAs. In p-type GaAs, oxidative decomposition takes place in the absence of light and the etching is isotropic and not limited to the area illuminated by radiation.
It is highly desirable to have an etching process which is anisotropic and can be directed to predetermined areas typically by illumination by radiation. Anisotropic photoetching is highly desirable in modern fabrication procedures for semiconductors because of reduced dimensions of many recently developed semiconductor devices, high precision requirements for these devices and simpler, less costly, and more rapid manufacturing procedures possible using such an etching procedure.